Multi-layer golf ball

ABSTRACT

The present invention is directed to an improved multi-layer golf ball comprising a core, an inner cover layer and an outer cover layer. The inner cover layer is comprised of a high acid ionomer or ionomer blend which may or may not include a filler such as zinc-stearate. The outer cover layer is comprised of a soft, very low modulus ionomer or ionomer blend, or a non-ionomeric thermoplastic elastomer such as polyurethane, polyester or polyesteramide. The resulting multi-layered golf ball of the present invention provides for enhanced distance without sacrificing playability or durability when compared to known multi-layer golf balls.

This is a divisional of application Ser. No. 08/562,540 filed on Nov.20, 1995, abandoned, which is a continuation of application Ser. No.08/070,510 filed on Jun. 1, 1993, abandoned.

FIELD OF THE INVENTION

The present invention relates to golf balls and, more particularly, toimproved golf balls comprising multi-layer covers which have a hardinner layer and a relatively soft outer layer. The improved multi-layergolf balls provide for enhanced distance and durability properties whileat the same time offering the “feel” and spin characteristics associatedwith soft balata and balata-like covers of the prior art.

BACKGROUND OF THE INVENTION

Traditional golf ball covers have been comprised of balata or blends ofbalata with elastomeric or plastic materials; The traditional balatacovers are relatively soft and flexible. Upon impact, the soft balatacovers compress against the surface of the club producing high spin.Consequently, the soft and flexible balata covers provide an experiencedgolfer with the ability to apply a spin to control the ball in flight inorder to produce a draw or a fade, or a backspin which causes the ballto “bite” or stop abruptly on contact with the green. Moreover, the softbalata covers produce a soft “feel” to the low handicap player. Suchplayability properties (workability, feel, etc.) are particularlyimportant in short iron play with low swing speeds and are exploitedsignificantly by relatively skilled players.

Despite all the benefits of balata, balata covered golf balls are easilycut and/or damaged if mis-hit. Golf balls produced with balata orbalata-containing cover compositions therefore have a relatively shortlifespan.

As a result of this negative property, balata and its syntheticsubstitutes, trans-polybutadiene and transpolyisoprene, have beenessentially replaced as the cover materials of choice by new covermaterials comprising ionomeric resins.

Ionomeric resins are polymers containing interchain ionic: bonding. As aresult of their toughness, durability and flight: characteristics,various ionomeric resins sold by E. I. DuPont de Nemours & Company underthe trademark “Surlyn®” and more recently, by the Exxon Corporation (seeU. S. Pat. No. 4,911,451) under the trademarks “Escor®” and the tradename “Iotek”, have become the materials of choice for the constructionof golf ball covers over the traditional “balata” (transpolyisoprene,natural or synthetic) rubbers. As stated, the softer balata covers,although exhibiting enhanced playability properties, lack the durability(cut and abrasion resistance, fatigue endurance, etc.) propertiesrequired for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin, such asethylene, and a metal salt of an unsaturated carboxylic acid, such asacrylic acid, methacrylic acid, or maleic acid. Metal ions, such assodium or zinc, are used to neutralize some portion of the acidic groupin the copolymer resulting in a thermoplastic elastomer exhibitingenhanced properties, i.e. durability, etc., for golf ball coverconstruction over balata. However, some of the advantages gained inincreased durability have been offset to some degree by the decreasesproduced in playability. This is because although the ionomeric resinsare very durable, they tend to be very hard when utilized for golf ballcover construction, and thus lack the degree of softness required toimpart the spin necessary to control the ball in flight. Since theionomeric resins are harder than balata, the ionomeric resin covers donot compress as much against the face of the club upon impact, therebyproducing less spin. In addition, the harder and more durable ionomericresins lack the “feel” characteristic associated with the softer balatarelated covers.

As a result, while there are currently more than fifty (50) commercialgrades of ionomers available both from DuPont and Exxon, with a widerange of properties which vary according to the type and amount of metalcations, molecular weight, composition of the base resin (i.e., relativecontent of ethylene and methacrylic and/or acrylic acid groups) andadditive ingredients such as reinforcement agents, etc., a great deal ofresearch continues in order to develop a golf ball cover compositionexhibiting not only the improved impact resistance and carrying distanceproperties produced by the “hard” ionomeric resins, but also theplayability (i.e., “spin”, “feel”, etc.) characteristics previouslyassociated with the “soft” balata covers, properties which are stilldesired by the more skilled golfer.

Consequently, a number of two-piece (a solid resilient center or corewith a molded cover) and three-piece (a liquid or solid center,elastomeric winding about the center, and a molded cover) golf ballshave been produced by the present inventor and others to address theseneeds. The different types of materials utilized to formulate the cores,covers, etc. of these balls dramatically alters the balls' overallcharacteristics. In addition, multi-layered covers containing one ormore ionomer resins have also been formulated in an attempt to produce agolf ball having the overall distance, playability and durabilitycharacteristics desired.

This was addressed by Spalding & Evenflo Companies, Inc., the assigneeof the present invention, in U. S. Pat. No. 4,431,193 where amulti-layered golf ball is disclosed. In the '193 patent, a multi-layergolf ball is produced by initially molding a first cover layer on aspherical core and then adding a second layer. The first layer iscomprised of a hard, high flexural modulus resinous material such astype 1605 Surlyn® (now designated Surlyn® 8940). Type 1605 Surlyn®(Surlyn® 8940) is a sodium ion based low acid (less than or equal to 15weight percent:

methacrylic acid) ionomer resin having a flexural modulus of about51,000 psi. An outer layer of a comparatively soft, low flexural modulusresinous material such as type 1855 Surlyn® (now designated Surlyn®9020) is molded over the inner cover layer. Type 1855 Surlyn® (Surlyn®9020) is a zinc ion based low acid (10 weight percent methacrylic acid)ionomer resin having a flexural modulus f about 14,000 psi.

The '193 patent teaches that the hard, high flexural modulus resin whichcomprises the first layer provides for a gain in coefficient ofrestitution over the coefficient of restitution of the -core. Theincrease in the coefficient of restitution provides a ball which servesto attain or approach the maximum initial velocity limit of 255 feet persecond as provided by the United States Golf Association (U.S.G.A.)rules. The relatively soft, low flexural modulus outer layer providesessentially no gain in the coefficient of restitution but provides forthe advantageous “feel” and playing characteristics of a balata coveredgolf ball. Unfortunately, however, while a ball of the '193 patent doesexhibit enhanced playability characteristics with improved distance(i.e. enhanced C.O.R. values) over a number of other known multi-layeredballs, the ball suffers from poor cut resistance and relatively shortdistance (i.e. lower C.O.R. values) when compared to two-piece, singlecover layer balls. These undesirable properties make the ball producedin accordance with the '193 patent unacceptable by today'as standards,The present invention is directed to new multi-layer golf ballcompositions which provide for enhanced coefficient of restitution (i.e,enhanced resilience or carrying distance) and/or durability propertieswhen compared to the multi-layer balls found in the prior art, as wellas improved outer cover layer softness and durability. As such, theplayability characteristics (i.e., “feel”, “click”, “spin”, etc.) arenot diminished.

These and other objects and features of the invention will be apparentfrom the following summary and description of the invention, thedrawings and from the claims.

SUMMARY OF THE INVENTION

The present invention is directed to improved multi-layer golf ballcover compositions and the resulting multi-layer golf balls producedusing the improved compositions. The novel multi-layer golf ball coversof the present invention include a first or inner layer or ply of a highacid (greater than 16 weight percent acid) ionomer or ionomer blend andsecond or outer layer or ply comprised of a comparatively softer, lowmodulus ionomer, ionomer blend or other non-ionomeric thermoplasticelastomer such as polyurethane, a polyester elastomer such as Hytrel®polyester elastomer of E. I. DuPont de Nemours & Company, or apolyesteramide such as the Elf Atochem S. A. Pebax® polyesteramide.Preferably, the outer cover layer includes a blend of hard and soft lowacid (i.e. 16 weight percent acid or less) ionomers.

It has been found that the recently developed high acid ionomer basedinner layer, provides for a substantial increase in resilience (i.e.,enhanced distance) over known multi-layer covered balls. The softerouter layer provides for desirable “feel” and high spin rate whilemaintaining respectable resiliency. The soft outer layer allows thecover to deform more during impact and increases the area of contactbetween the club face and the cover, thereby imparting more spin on theball. As a result, the soft cover provides the ball with a balata-likefeel and playability characteristics with improved distance anddurability. Consequently, the overall combination of the inner and outercover layers results in a golf ball having enhanced resilience (improvedtravel distance) and durability (i.e. cut resistance, etc.)characteristics while maintaining and in many instances, improving theballs playability properties.

The combination of a high acid ionomer or ionomer blend inner coverlayer with a soft, relatively low modulus ionomer, ionomer blend orother non-ionomeric thermoplastic elastomer outer cover layer providesfor excellent overall coefficient of restitution (i.e., excellentresilience) because of the improved resiliency produced by the innercover layer. While some improvement in resiliency is also produced bythe outer cover layer, the outer cover layer generally provides for amore desirable feel and high spin, particularly at lower swing speedswith highly lofted clubs such as half wedge shots.

Two principal properties involved in golf ball performance areresilience and hardness. Resilience is determined by the coefficient ofrestitution (C.O.R.), the constant “e” which is the ratio of therelative velocity of two elastic spheres after direct impact to thatbefore impact. As a result, the coefficient of restitution (“e”) canvary from 0 to 1, with 1 being equivalent to an elastic collision and 0being equivalent to an inelastic collision.

Resilience (C.O.R.), along with additional factors such as club headspeed, angle of trajectory and ball configuration (i.e., dimple pattern)generally determine the distance a ball will travel when hit. Since clubhead speed and the angle of trajectory are factors not easilycontrollable by a manufacturer, factors of concern among manufacturersare the coefficient of restitution (C.O.R.) and the surfaceconfiguration of the ball.

The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover. Inballs containing a wound core (i.e., balls comprising a liquid or solidcenter, elastic windings, and a cover), the coefficient of restitutionis a function of not only the composition of the center and cover, butalso the composition and tension of the elastomeric windings. Althoughboth the core and the cover contribute to the coefficient ofrestitution, the present invention is directed to the enhancedcoefficient of restitution (and thus travel distance) which is affectedby the cover composition.

In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball'as incoming and outgoing velocityelectronically. As mentioned above, the coefficient of restitution isthe ratio of the outgoing velocity to the incoming velocity. Thecoefficient of restitution must be carefully controlled in allcommercial golf balls in order, for the ball to be within thespecifications regulated by the United States Golf Association(U.S.G.A.). Along this line, the U.S.G.A. standards indicate that a“regulation” ball cannot have an initial velocity (i.e., the speed offthe club) exceeding 255 feet per second. Since the coefficient ofrestitution of a ball is related to the ball'as initial velocity, it ishighly desirable to produce a ball having sufficiently high coefficientof restitution to closely approach the U.S.G.A. limit on initialvelocity, while having an ample degree of softness (i.e., hardness) toproduce enhanced playability (i.e., spin, etc.).

The hardness of the ball is the second principal property involved inthe performance of a golf ball. The hardness of the ball can affect theplayability of the ball on striking and the sound or “click” produced.Hardness is determined by the deformation (i.e., compression) of theball under various load conditions applied across the ball'as diameter(i.e., the lower the compression value, the harder the material). Asindicated in U.S. Pat. No. 4,674,751, softer covers permit theaccomplished golfer to impart proper spin. This is because the softercovers deform on impact significantly more than balls having “harder”ionomeric resin covers. As a result, the better player is allowed toimpart fade, draw or backspin to the ball thereby enhancing playability.Such properties may be determined by various spin rate tests such as the“nine iron” spin rate test described below in the Examples.

Accordingly, the present invention is directed to an improvedmulti-layer cover which produces, upon molding each layer around a core(preferably a solid core) to formulate a multi-layer cover, a golf ballexhibiting enhanced distance (i.e., resilience) without adverselyaffecting, and in many instances, improving the ball'as playability(hardness/softness) and/or durability (i.e., cut resistance, fatigueresistance, etc.) characteristics.

These and other objects and features of the invention will be apparentfrom the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a golf ball embodying the inventionillustrating a core 10 and a cover 12 consisting of an inner layer 14and an outer layer 16 having dimples 18; and

FIG. 2 is a diametrical cross-sectional view of a golf ball of theinvention having a core 10 and a cover 12 made of an inner layer 14 andan outer layer 16 having dimple 18.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to improved multi-layer golf balls,particularly a golf ball comprising a multi-layered cover 12 over asolid core 10, and method for making same.

The multi-layered cover 12 comprises two layers: a first: or inner layeror ply 14 and a second or outer layer or ply 16. The inner layer 14 iscomprised of a high acid (i.e. greater than 16 weight percent acid)ionomer resin or high acid ionomer blend. Preferably, the inner layer iscomprised of a blend of two or more high acid (i.e. at least 16 weightpercent acid) ionomer resin neutralized to various extents by differentmetal cations. The inner cover layer may or may not include a metalstearate (e.g., zinc stearate) or other metal fatty acid salt. Thepurpose of the metal stearate or other metal fatty acid salt is to lowerthe cost of production without affecting the overall performance of thefinished golf ball.

The inner layer compositions include the high acid ionomers such asthose recently developed by E. I. DuPont de Nemours & Company under thetrademark “Surlyn®” and by Exxon Corporation under the trademark“Escors” or tradename “Iotek”, or blends thereof. Examples ofcompositions which may be used as the inner layer herein are set forthin detail in copending U. S. Ser. No. 07/776,803 filed Oct. 15, 1991,and Ser. No. 07/901,660 filed Jun. 19, 1992, both incorporated herein byreference. Of course, the inner layer high acid ionomer compositions arenot limited in any way to those compositions set forth in said copendingapplications. For example, the high acid ionomer resins recentlydeveloped by Spalding & Evenflo Companies, Inc., the assignee of thepresent invention, and disclosed in U.S. Ser. No. 07/901,680, filed Jun.19, 1992, incorporated herein by reference, may also be utilizedto-produce the inner layer of the multi-layer cover used in the presentinvention.

The high acid ionomers which may be suitable for use in formulating theinner layer compositions of the subject invention are ionic copolymerswhich are the metal, i.e., sodium, zinc, magnesium, etc., salts of thereaction product of an olefin having from about 2 to 8 carbon atoms andan unsaturated monocarboxylic acid having from about 3 to 8 carbonatoms. Preferably, the ionomeric resins are copolymers of ethylene andeither acrylic or methacrylic acid. In some circumstances, an additionalcomonomer such as an acrylate ester (i.e., iso- or n-butylacrylate,etc.) can also be included to produce a softer terpolymer. Thecarboxylic acid groups of the copolymer are partially neutralized (i.e.,approximately 10-75%, preferably 30-70%) by the metal ions. Each of thehigh acid ionomer resins which may be included in the inner layer covercompositions of the invention contains greater than about 16% by weightof a carboxylic acid, preferably from about 17% to about 25% by weightof a carboxylic acid, more preferably from about 18.5% to about 21.5% byweight of a carboxylic acid.

Although the inner layer cover composition preferably includes a highacid ionomeric resin and the scope of the patent embraces all known highacid ionomeric resins falling within the parameters set forth above,only a relatively limited number of these high acid ionomeric resinshave recently become commercially available.

The high acid ionomeric resins available from Exxon under thedesignation “Escor®” and or “Iotek”, are somewhat similar to the highacid ionomeric resins available under the “Surlyn®” trademark. However,since the Escor®/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

Examples of the high acid methacrylic acid based ionomers found suitablefor use in accordance with this invention include Surlyn® AD-8422(sodium cation), Surlyn® 8162 (zinc cation), Surlyn® SEP-503-1 (zinccation), and Surlyn® SEP-503-2 (magnesium cation). According to DuPont,all of these ionomers contain from about 18.5 to about 21.5% by weightmethacrylic acid.

More particularly, Surlyn® AD-8422 is currently commercially availablefrom DuPont in a number of different grades (i.e., AD-8422-2, AD-8422-3,AD-8422-5, etc.) based upon differences in melt index. According toDuPont, Surlyn® AD-8422 offers the following general properties whencompared to Surlyn®8920, the stiffest, hardest of all on the low acidgrades (referred to as “hard” ionomers in U.S. Pat. No. 4,884,814):

LOW ACID HIGH ACID (15 wt % Acid) (>20 wt % Acid) SURLYN ® SURLYN ®SURLYN ® 8920 8422-2 8422-3 IONOMER Cation Na Na Na Melt Index 1.2 2.81.0 Sodium, Wt % 2.3 1.9 2.4 Base Resin MI 60 60 60 MP¹, ° C. 88 86 85FP¹, ° C. 47 48.5 45 COMPRESSION MOLDING² Tensile Break, 4350 4190 5330psi Yield, psi 2880 3670 3590 Elongation, % 315 263 289 Flex Mod, 53.276.4 88.3 K psi Shore D 66 67 68 hardness ¹DSC second heat, 10° C./minheating rate. ²Samples compression molded at 150° C. annealed 24 hoursat 60° C. 8422-2, -3 were homogenized at 190° C. before molding.

In comparing Surlyn® 8920 to Surlyn® 8422-2 and Surlyn® 8422-3, it isnoted that the high acid Surlyn® 8422-2 and 8422-3 ionomers have ahigher tensile yield, lower elongation, slightly higher Shore D hardnessand much higher flexural modulus. Surlyn® 8920 contains 15 weightpercent methacrylic acid and is 59% neutralized with sodium.

In addition, Surlyn® SEP-503-1 (zinc cation) and Surlyn® SEP-503-2(magnesium cation) are high acid zinc and magnesium versions of theSurlyn® AD 8422 high acid ionomers. When compared to the Surlyn® AD 8422high acid ionomers, the Surlyn SEP-503-1 and SEP-503-2 ionomers can bedefined as follows:

Surlyn ® Ionomer Ion Melt Index Neutralization % AD 8422-3 Na 1.0 45 SEP503-1 Zn 0.8 38 SEP 503-2 Mg 1.8 43

Furthermore, Surlyn® 8162 is a zinc cation ionomer resin containingapproximately 20% by weight (i.e. 18.5-21.5% weight) methacrylic acidcopolymer that has been 30-70% neutralized. Surlyn® 8162 is currentlycommercially available from DuPont.

Examples of the high acid acrylic acid based ionomers suitable for usein the present invention also include the Escor® or Iotek high acidethylene acrylic acid ionomers produced by Exxon. In this regard, Escor®or Iotek 959 is a sodium ion neutralized ethylene-acrylic neutralizedethylene-acrylic acid copolymer. According to Exxon, Ioteks 959 and 960contain from about 19.0 to about 21.0% by weight acrylic acid withapproximately 30 to about 70 percent of the acid groups neutralized withsodium and zinc ions, respectively. The physical properties of thesehigh acid acrylic acid based ionomers are as follows:

ESCOR ® ESCOR ® PROPERTY (IOTEK) 959 (IOTEK) 960 Melt Index, g/10 min2.0 1.8 Cation Sodium Zinc Melting Point, ° F. 172 174 Vicat SofteningPoint, ° F. 130 131 Tensile @ Break, pst 4600 3500 Elongatian @ Break, %325 430 Hardness, Shore D 66 57 Flexural Modulus, psi 66,000 27,000

Furthermore, as a result of the development by the inventor of a numberof new high acid ionomers neutralized to various extents by severaldifferent types of metal cations, such as by manganese, lithium,potassium, calcium and nickel cations, several new high acid ionomersand/or high acid ionomer blends besides sodium, zinc and magnesium highacid ionomers or ionomer blends are now available for golf ball coverproduction. It has been found that these new cation neutralized highacid ionomer blends produce inner cover layer compositions exhibitingenhanced hardness and resilience due to synergies which occur duringprocessing. Consequently, the metal cation neutralized high acid ionomerresins recently produced can be blended to produce substantially harderinner cover layers for multi-layered golf balls having higher C.O.R.'asthan those produced by the low acid ionomer inner cover compositionspresently commercially available.

More particularly, several new metal cation neutralized high acidionomer resins have been produced by the inventor by neutralizing, tovarious extents, high acid copolymers of an alpha-olefin and an alpha,beta-unsaturated carboxylic acid with a wide variety of different metalcation salts. This discovery is the subject matter of U.S. applicationSer. No. 901,680, incorporated herein by reference. It has been foundthat numerous new metal cation neutralized high acid ionomer resins canbe obtained by reacting a high acid copolymer (i.e. a copolymercontaining greater than 16% by weight acid, preferably from about 17 toabout 25 weight percent acid, and more preferably about 20 weightpercent acid), with a metal cation salt capable of ionizing orneutralizing the copolymer to the extent desired (i.e. from about 10% to90%).

The base copolymer is made up of greater than 16% by weight of an alpha,beta-unsaturated carboxylic acid and an alpha-olefin. Optionally, asoftening comonomer can be included in the copolymer. Generally, thealpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene,and the unsaturated carboxylic acid is a carboxylic acid having fromabout 3 to 8 carbons. Examples of such acids include acrylic acid,methacrylic, acid, ethacrylic acid, chloroacrylic acid, crotonic acid,maleic acid, fumaric acid, and itaconic acid, with acrylic acid beingpreferred.

The softening comonomer that can be optionally included in the inventionmay be selected from the group consisting of vinyl esters of aliphaticcarboxylic acids wherein the acids have 2 to 10 carbon atoms, vinylethers wherein the alkyl groups contains 1 to 10 carbon atoms, and alkylacrylates or methacrylates wherein the alkyl group contains 1 to 10carbon atoms. Suitable softening comonomers include vinyl acetate,methyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, butyl acrylate, butyl methacrylate, or the like.

Consequently, examples of a number of copolymers suitable for use toproduce the high acid ionomers included in the present inventioninclude, but are not limited to, high acid embodiments of anethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer,an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer,an ethylene/methacrylic acid/vinyl acetate copolymer, anethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymerbroadly contains greater than 16% by weight unsaturated carboxylicacid., from about 30 to about 83% by weight ethylene and from 0 to about40% by weight of a softening comonomer. Preferably, the copolymercontains about 20% by weight unsaturated carboxylic acid and about 80%by weight ethylene. Most preferably, the copolymer contains about 20%acrylic acid with the remainder being ethylene.

Along these lines, examples of the preferred high acid base copolymerswhich fulfill the criteria set forth above, are a series ofethylene-acrylic copolymers which are commercially available from TheDow Chemical Company, Midland, Mich., under the “Primacor” designation.These high acid base copolymers exhibit the typical properties set forthbelow in Table 1.

TABLE 1 Typical Properties of Primacor Ethylene-Acrylic Acid CopolymersMELT TENSILE FLEXURAL VICAT PERCENT DENSITY, INDEX YD. ST MODULUS SOFTPT SHORE D GRADE ACID glcc g/10 min (psi) (psi) (° C.) HARDNESS ASTMD-792 D-1238 D-638 D-790 D-1525 D-2240 5980 20.0 0.958 300.0 - 4800 4350 5990 20.0 0.955 1300.0 650 2600 40 42 5990 20.0 0.955 1300.0 650 320040 42 5981 20.0 0.960 300.0 900 3200 46 48 5981 20.0 0.960 300.0 9003200 46 48 5983 20.0 0.958 500.0 850 3100 44 45 5991 20.0 0.953 2600.0635 2600 38 40 ¹The Melt Index values are obtained according to ASTMD-1238, at 190° C.

Due to the high molecular weight of the Primacor 5981 grade of theethylene-acrylic acid copolymer, this copolymer is the more preferredgrade utilized in the invention.

The metal cation salts utilized in the invention are those salts whichprovide the metal cations capable of neutralizing, to various extents,the carboxylic acid groups of the high acid copolymer. These includeacetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium,potassium, nickel, magnesium, and manganese.

Examples of such lithium ion sources are lithium hydroxide monohydrate,lithium hydroxide, lithium oxide and lithium acetate. Sources for thecalcium ion include calcium hydroxide, calcium acetate and calciumoxide. Suitable zinc ion sources are zinc acetate dihydrate and zincacetate, a blend of zinc oxide and acetic acid. Examples of sodium ionsources are sodium hydroxide and sodium acetate. Sources for thepotassium ion include potassium hydroxide and potassium acetate.Suitable nickel ion sources are nickel acetate, nickel oxide and nickelhydroxide. Sources of magnesium include magnesium oxide, magnesiumhydroxide, magnesium acetate. Sources of manganese include manganeseacetate and manganese oxide.

The new metal cation neutralized high acid ionomer resins are producedby reacting the high acid base copolymer with various amounts of themetal cation salts above the crystalline melting point of the copolymer,such as at a temperature from about 200° F. to about 500° F., preferablyfrom about 250° F. to about 350° F. under high shear conditions at apressure of from about 10 psi to 10,000 psi. Other well known blendingtechniques may also be used. The amount of metal cation salt utilized toproduce the new metal cation neutralized high acid based ionomer resinsis the quantity which provides a sufficient amount of the metal cationsto neutralize the desired percentage of the carboxylic acid groups inthe high acid copolymer. The extent of neutralization is generally fromabout 10% to about 90%.

As indicated below in Table 2 and more specifically in Example 1 in U.S.application Ser. No. 901,680, a number of new types of metal cationneutralized high acid ionomers can be obtained from the above indicatedprocess. These include new high acid ionomer resins neutralized tovarious extents with manganese, lithium, potassium, calcium, and nickelcations. In addition, when a high acid ethylene/acrylic acid copolymeris utilized as the base copolymer component of the invention and thiscomponent is subsequently neutralized to various extents with the metalcation salts producing acrylic acid based high acid ionomer resinsneutralized with cations such as sodium, potassium, lithium, zinc,magnesium, manganese, calcium and nickel, several new cation neutralizedacrylic acid based high acid ionomer resins are produced.

TABLE 2 Formulation Wt-% Wt-% Melt Shore D No. Catian SaltNeutralization Index C.O.R. Hardness  1 (NaOH) 6.98 67.5 0.9 .804 71  2(NaOH) 5.66 54.0 2.4 .808 73  3 (NaOH) 3.84 35.9 12.2 .812 69  4 (NaOH)2.91 27.0 17.5 .812 (brittle)  5 (MnAc) 19.6 71.7 7.5 .809 73  6 (MnAc)23.1 88.3 3.5 .814 77  7 (MnAc) 15.3 53.0 7.5 .810 72  8 (MnAc) 26.5 1060.7 .813 (brittle)  9 (LiOH) 4.54 71.3 0.6 .810 74 10 (LiOH) 3.38 52.54.2 .818 72 11 (LiOH) 2.34 35.9 18.6 .815 72 12 (KOH) 5.30 36.0 19.3Broke 70 13 (KOH) 8.26 57.9 7.18 .804 70 14 (KOH) 10.7 77.0 4.3 .801 6715 (ZnAc) 17.9 71.5 0.2 .806 71 16 (ZnAc) 13.9 53.0 0.9 .797 69 17(ZnAc) 9.91 36.1 3.4 .793 67 18 (MgAc) 17.4 70.7 2.8 .814 74 19 (MgAc)20.6 87.1 1.5 .815 76 20 (MgAc) 13.8 53.8 4.1 .814 74 21 (CaAc) 13.269.2 1.1 .813 74 22 (CaAc) 7.12 34.9 10.1 .808 70 Controls: 50/50 Blendof Ioteks 8000/7030 C.O.R. = .810/65 Shore D Hardness DuPont High AcidSurlyn ® 8422 (Na) C.O.R. = .811/70 Shore D Hardness DuPont High AcidSurlyn ® 8162 (Zn) C.O.R. = .807/65 Shore D Hardness Exxon High AcidIotek Ex-960 (Zn) C.O.R. = .796/65 Shore D Hardness Wt-% Wt-% MeltFormulation No. Cation Salt Neutralization Index C.O.R. 23 (MgO) 2.9153.5 2.5 .813 24 (MgO) 3.85 71.5 2.8 .808 25 (MgO) 4.76 89.3 1.1 .809 26(MgO) 1.96 35.7 7.5 .815 Control for Formulations 23-26 is 50/50 Iotek8000/7030, C.O.R. = .814, Formulation 26 C.O.R. was normalized to thatcontrol accordingly Formulation Wt-% Wt-% Melt Shore D No. Cation SaltNeutralization Index C.O.R. Hardness 27 (NiAc) 13.04 61.1 0.2 .802 71 28(NiAc) 10.71 48.9 0.5 .799 72 29 (NiAc) 8.26 36.7 1.8 .796 69 30 (NiAc)5.66 24.4 7.5 .786 64 Control for Formulation Nos. 27-30 is 50/50 Iotek8000/7030, C.O.R. = .807

When compared to low acid versions of similar cation neutralized ionomerresins, the new metal cation neutralized high acid ionomer resinsexhibit enhanced hardness, modulus and resilience characteristics. Theseare properties that are particularly desirable in a number ofthermoplastic fields, including the field of golf ball manufacturing.

When utilized in the construction of the inner layer of a multi-layeredgolf ball, it has been found that the new acrylic acid based high acidionomers extend the range of hardness beyond that previously obtainablewhile maintaining the beneficial properties (i.e. durability, click,feel, etc.) of the softer low acid ionomer covered balls, such as ballsproduced utilizing the low acid ionomers disclosed in U.S. Pat. Nos.4,884,814 and 4,911,451.

Moreover, as a result of the development of a number of new acrylic acidbased high acid ionomer resins neutralized to various extents by severaldifferent types of metal cations, such as manganese, lithium, potassium,calcium and nickel cations, several new ionomers or ionomer blends arenow available for production of an inner cover layer of a multi-layeredgolf ball. By using these high acid ionomer resins, harder, stifferinner cover layers having higher C.O.R.s, and thus longer distance, canbe obtained.

More preferably, it has been found that when two or more of theabove-indicated high acid ionomers, particularly blends of sodium andzinc high acid ionomers, are processed to produce the covers ofmulti-layered golf balls, (i.e., the inner cover layer herein) theresulting golf balls will travel further than previously knownmulti-layered golf balls produced with low acid ionomer resin covers dueto the balls' enhanced coefficient of restitution values.

For example, the multi-layer golf ball taught in U.S. Pat. No. 4,650,193does not incorporate a high acid ionomeric resin in the inner coverlayer. As will be set forth below in the Examples, the coefficient ofrestitution of the golf ball having an inner layer taught by the '193patent (i.e., inner layer composition “D” in the Examples) issubstantially lower than the coefficient of restitution of the remainingcompositions. In addition, the multi-layered ball disclosed in the '193patent suffers substantially in durability in comparison with thepresent invention.

With respect to the outer layer 16 of the multi-layered cover of thepresent invention, the outer cover layer is comparatively softer thanthe high acid ionomer based inner layer. The softness provides for thefeel and playability characteristics typically associated with balata orbalata-blend balls. The outer layer or ply is comprised of a relativelysoft, low modulus (about 1,000 psi to about 10,000 psi) and low acid(less than 16 weight percent acid) ionomer, ionomer blend or anon-ionomeric thermoplastic elastomer such as, but not limited to, apolyurethane, a polyester elastomer such as that marketed by DuPontunder the trademark Hytrel®, or a polyester amide such as that marketedby Elf Atochem S. A. under the trademark Pebax®. The outer layer isfairly thin (i.e. from about 0.010 to about 0.050 in thickness, moredesirably 0.03 inches in thickness for a 1.680 inch ball), but thickenough to achieve desired playability characteristics while minimizingexpense.

Preferably, the outer layer includes a blend of hard and soft (low acid)ionomer resins such as those described in U.S. Pat. Nos. 4,884,814 and5,120,791, both incorporated herein by reference. Specifically, adesirable material for use in molding the outer layer comprises a blendof a high modulus (hard) ionomer with a low modulus (soft) ionomer toform a base ionomer mixture. A high modulus ionomer herein is one whichmeasures from about 15,000 to about 70,000 psi as measured in accordancewith ASTM method D-790. The hardness may be defined as at least 50 onthe Shore D scale as measured in accordance with ASTM method D-2240.

A low modulus ionomer suitable for use in the outer layer blend has aflexural modulus measuring from about 1,000 to about 10,000 psi, with ahardness of about 20 to about 40 on the Shore D scale.

The hard ionomer resins utilized to produce the outer cover layercomposition hard/soft blends include ionic copolymers which are thesodium, zinc, magnesium or lithium salts of the reaction product of anolefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylicacid having from 3 to 8 carbon atoms. The carboxylic acid groups of thecopolymer may be totally or partially (i.e. approximately 15-75 percent)neutralized.

The hard ionomeric resins are likely copolymers of ethylene and eitheracrylic and/or methacrylic acid, with copolymers of ethylene and acrylicacid being the most preferred. Two or more types of hard ionomericresins may be blended into the outer cover layer compositions in orderto produce the desired properties of the resulting golf balls.

As discussed earlier herein, the hard ionomeric resins introduced underthe designation Escor® and sold under the designation “Iotek” aresomewhat similar to the hard ionomeric resins sold under the Surlyn®trademark. However, since the “Iotek” ionomeric resins are sodium orzinc salts of poly(ethylene-acrylic acid) and the Surlyn® resins arezinc or sodium salts of poly(ethylene-methacrylic acid) some distinctdifferences in properties exist. As more specifically indicated in thedata set forth below, the hard “Iotek” resins (i.e., the acrylic acidbased hard ionomer resins) are the more preferred hard resins for use informulating the outer layer blends for use in the present invention. Inaddition, various blends of “Iotek” and Surlyn® hard ionomeric resins,as well as other available ionomeric resins, may be utilized in thepresent invention in a similar manner.

Examples of commercially available hard ionomeric resins which may beused in the present invention in formulating the outer cover blendsinclude the hard sodium ionic copolymer sold under the trademarkSurlyn®8940 and the hard zinc ionic copolymer sold under the trademarkSurlyn®9910. Surlyn®8940 is a copolymer of ethylene with methacrylicacid and about 15 weight percent acid which is about 29 percentneutralized with sodium ions. This resin has an average melt flow indexof about 2.8. Surlyn®9910 is a copolymer of ethylene and methacrylicacid with about 15 weight percent acid which is about 58 percentneutralized with zinc ions. The average melt flow index of Surlyn®9910is about 0.7. The typical properties of Surlyn®9910 and 8940 are setforth below in Table 3:

TABLE 3 Typical Properties of Commercially Available Hard Surlyn ®Resins Suitable for Use in the Outer Layer Blends of the PresentInvention 8940 9910 8920 8528 9970 9730 Cation Type ASTM D Sodium ZincSodium Sodium Zinc Zinc Melt flow index, D-1238 2.8 0.7 0.9 1.3 14.0 1.6gms/10 min. Specific Gravity, D-792 0.95 0.97 0.95 0.94 0.95 0.95 g/cm³Hardness, Shore D D-2240 66 64 66 60 62 63 Tensile Strength, D-638 (4.8)(3.6) (5.4) (4.2) (3.2) (4.1) (kspi), MPa 33.1 24.8 37.2 29.0 22.0 28.0Elongation, % D-638 470 290 350 450 460 460 Flexural Modulus, D-790 (51)(48) (55) (32) (28) (30) (kpsi) MPa 350 330 380 220 190 210 TensileImpact (23° C.) D-1822s 1020 1020 865 1160 760 1240 KJ/m₂ (ft. -lbs./in²) (485) (485) (410) (550) (360) (590) Vicat Temperature, ° C.D-1525 63 62 58 73 61 73

Examples of the more pertinent acrylic acid based hard ionomer resinsuitable for use in the present outer cover composition sold under the“Iotek” tradename by the Exxon Corporation include Iotek 4000, Iotek4010, Iotek 8000, Iotek 8020 and Iotek 8030. The typical properties ofthese and other Iotek hard ionomers suited for use in formulating theouter layer cover composition are set forth below in Table 4:

TABLE 4 Typical Properties of Iotek Ionomers Resin ASTM PropertiesMethod Units 4000 4010 8000 8020 8030 Cation type zinc zinc sodiumsodium sodium Melt Index D-1238 g/10 min. 2.5 1.5 0.8 1.6 2.8 DensityD-1505 kg/m³ 963 963 954 960 960 Melting Potnt D-3417 ° C. 90 90 90 87.587.5 Crystalization Point D-3417 ° C. 62 64 56 53 55 Vicat SofteningPoint D-1525 ° C. 62 63 61 64 67 % Weight Acrylic Acid 16 11 % of AcidGroups cation neutralized 30 40 Plaque Properties (3 mm thick,compression molded) Tensile at break D-638 MPa 24 26 36 31.5 28 Yieldpoint D-638 MPa none none 21 21 23 Elongation at break D-638 % 395 420350 410 395 1% Secant modulus D-638 MFa 160 160 300 350 390 ShoreHardness D D-2240 — 55 55 61 58 59 Film Properties (50 micron film 2.2:1Blow-up ratio) Tensile at Break MD D-882 MPa 41 39 42 52 47.4 TD D-882MPa 37 38 38 38 40.5 Yield point MD D-882 MPa 15 17 17 23 21.6 TD D-882MPa 14 15 15 21 20.7 Elongation at Break MD D-882 % 310 270 260 295 305TD D-882 % 360 340 280 340 345 1% Secant modulus MD D-882 MPa 210 215390 380 380 TD D-882 MPa 200 225 380 350 345 Dart Drop Impact D-1709g/micron 12.4 12.5 20.3 Resin ASTM Properties Method Units 7010 70207030 Cation type zinc zinc zinc Melt Index D-1238 g/10 min. 0.8 1.5 2.5Density D-1505 kg/m³ 960 960 960 Melting Point D-3417 ° C. 90 90 90Crystalization D-3417 ° C. — — — Point Vicat Softening D-1525 ° C. 60 6362.5 Point % Weight Acrylic Acld % of Acid Groups — — — CationNeutralized Plaque Properties (3 mm thick, compression molded) Tensileat break D-638 MPa 38 38 38 Yield Point D-638 MPa none none noneElongation at break D-638 % 500 420 395 1% Secant modulus D-638 MPa — —— Shore Hardness D D-2240 — 57 55 55

Comparatively, soft ionomers are used in formulating the hard/softblends of the outer cover composition. These ionomers include acrylicacid based soft ionomers. They are generally characterized as comprisingSodium or zinc salts of a terpolymer of an olefin having from about 2 to8 carbon atoms, acrylic acid, and an unsaturated monomer of the acrylateester class having from 1 to 21 carbon atoms. The soft ionomer ispreferably a zinc based ionomer made from an acrylic acid base polymerin an unsaturated monomer of t he acrylate ester class. The soft (lowmodulus) ionomers have a hardness from about 20 to about 40 as measuredon the Shore D scale and a flexural modulus from about 1,000 to about10,000, as measured in accordance with ASTM method D-790.

Certain ethylene-acrylic acid based soft ionomer resins developed by theExxon Corporation under the designation “Iotek 7520” (referred toexperimentally by differences in neutralization and melt indexes as LDX195, LDX 196, LDX 218 and LDX 219) may be combined with known hardionomers such as those indicated above to produce the outer cover. Thecombination produces higher C.O.R.s at equal or softer hardness, highermelt flow (which corresponds to improved, more efficient molding, i.e.,fewer rejects) as well as significant cost savings versus the outerlayer of multi-layer balls produced by other known hard-soft ionomerblends as a result of the lower overall raw materials costs and improvedyields.

While the exact chemical composition of the resins to be sold by Exxonunder the designation Iotek 7520 is considered by Exxon to beconfidential and proprietary information, Exxon'as experimental productdata sheet lists the following physical properties of the ethyleneacrylic acid zinc ionomer developed by Exxon:

TABLE 5 Property ASTM Method Units Typical Value Physical Properties ofIotek 7520 Melt Index D-1238 g/10 min. 2 Density D-1505 kg/m³ 0.962Cation Zinc Melting Point D-3417 ° C. 66 Crystallization D-3417 ° C. 49Point Vicat softening D-1525 ° C. 42 Point Plaque Properties (2 mm thickCompression Molded Plaques) Tensile at Break D-638 MPa 10 Yield PointD-638 MPa None Elongation at Break D-638 % 760 1% Secant Modulus D-638MPa 22 Shore D Hardness D-2240 32 Flexural Modulus D-790 MPa 26 ZwickRebond ISO 4862 % 52 De Mattia Flex D-430 Cycles >5000 Resistance

In addition, test data collected by the inventor indicates that Iotek7520 resins have Shore D hardnesses of about 32 to 36 (per ASTM D-2240),melt flow indexes of 3±0.5 g/10 min (at 190° C. per ASTM D-1288), and aflexural modulus of about 2500-3500 psi (per ASTM D-790). Furthermore,testing by an independent testing laboratory by pyrolysis massspectrometry indicates that Iotek 7520 resins are generally zinc saltsof a terpolymer of ethylene, acrylic acid, and methyl acrylate.

Furthermore, the inventor has found that a newly developed grade of anacrylic acid based soft ionomer available from the Exxon Corporationunder the designation Iotek 7510, is also effective, when combined withthe hard ionomers indicated above in producing golf ball coversexhibiting higher C.O.R. values at equal or softer hardness than thoseproduced by known hard-soft ionomer blends. In this regard, Iotek 7510has the advantages (i.e. improved flow, higher C.O.R. values at equalhardness, increased clarity, etc.) produced by the Iotek 7520 resin whencompared to the methacrylic acid base soft ionomers known in the art(such as the Surlyn 8625 and the Surlyn 8629 combinations disclosed inU.S. Pat. No. 4,884,814).

In addition, Iotek 7510, when compared to Iotek 7520, produces slightlyhigher C.O.R. valves at equal softness/hardness due to the Iotek 7510'ashigher hardness and neutralization. Similarly, Iotek 7510 producesbetter release properties (from the mold cavities) due to its slightlyhigher stiffness and lower flow rate than Iotek 7520. This is importantin production where the soft covered balls tend to have lower yieldscaused by sticking in the molds and subsequent punched pin marks fromthe knockouts.

According to Exxon, Iotek 7510 is of similar chemical composition asIotek 7520 (i.e. a zinc salt of a terpoloymer of ethylene, acrylic acid,and methyl acrylate) but is more highly neutralized. Based upon FTIRanalysis, Iotek 7520 is estimated to be about 30-40 wt.-% neutralizedand Iotek 7510 is estimated to be about 40-60 wt.-% neutralized. Thetypical properties of Iotek 7510 in comparison of those of Iotek 7520are set forth below:

TABLE 6 Physical Properties of Iotek 7510 in Comparison to Iotek 7520IOTEK 7520 IOTEK 7510 MI, g/10 min 2.0 0.8 Density, g/cc 0.96 0.97Melting Point, ° F. 151 149 Vicat Softening Point, ° F. 108 109 FlexModulus, psi 3800 5300 Tensile Strength, psi 1450 1750 Elongation, % 760690 Hardness, Shore D 32 35

It has been determined that when hard/soft ionomer blends are used forthe outer cover layer, good results are achieved when the relativecombination is in a range of about 90 to about 10 percent hard ionomerand about 10 to about 90 percent soft ionomer. The results are improvedby adjusting the range to about 75 to 25 percent hard ionomer and 25 to75 percent soft ionomer. Even better results are noted at relativeranges of about 60 to 90 percent hard ionomer resin and about 40 to 60percent soft ionomer resin.

Specific formulations which may be used in the cover composition areincluded in the examples set forth in U.S. Pat. No. 5,120,791 and4,884,814. The present invention is in no way limited to those examples.

Moreover, in alternative embodiments, the outer cover layer formulationmay also comprise a soft, low modulus non-ionomeric thermoplasticelastomer including a polyester polyurethane such as B. F. GoodrichCompany'as Estanes polyester polyurethane X-4517. According to B. F.Goodrich, Estane® X-4517 has the following properties:

Properties of Estane ® X-4517 Tensile 1430 100% 815 200% 1024 300% 1193Elongation 641 Youngs Modulus 1826 Hardness A/D 88/39 Dayshore Rebound59 Solubility in Water Insoluble Melt processing temperature >350° F.(>177° C.) Specific Gravity (H₂O = 1) 1.1-1.3

Other soft, relatively low modulus non-ionomeric thermoplasticelastomers may also be utilized to produce the outer cover layer as longas the non-ionomeric thermoplastic elastomers produce the playabilityand durability characteristics desired without adversely effecting theenhanced travel distance characteristic produced by the high acidionomer resin composition. These include, but are not limited tothermoplastic polyurethanes such as: Texin thermoplastic polyurethanesfrom Mobay Chemical Co. and the Pellethane thermoplastic polyurethanesfrom Dow Chemical Co.; Ionomer/rubber blends such as those in SpaldingU.S. Pat. Nos. 4,986,545; 5,098,105 and 5,187,013; and, Hytrel polyesterelastomers from DuPont and pebax polyesteramides from Elf Atochem S. A.

In preparing golf balls in accordance with the present invention, a hardinner cover layer is molded (by injection molding or by compressionmolding) about a core (preferably a solid core). A comparatively softerouter layer is molded over the inner layer.

The conventional solid core is about 1.545 inches in diameter, althoughit can range from about 1.495 to about 1.575 inches. Conventional solidcores are typically compression molded from a slug of uncured or lightlycured elastomer composition comprising a high cis content polybutadieneand a metal salt of an α, β, ethylenically unsaturated carboxylic acidsuch as zinc mono or diacrylate or methacrylate. To achieve highercoefficients of restitution in the core, the manufacturer may includefillers such as small amounts of a metal oxide such as zinc oxide. Inaddition, larger amounts of metal oxide than those that are needed toachieve the desired coefficient are often included in conventional coresin order to increase the core weight so that the finished ball moreclosely approaches the U.S.G.A. upper weight limit of 1.620 ounces.Other materials may be used in the core composition including compatiblerubbers or ionomers, and low molecular weight fatty acids such asstearic acid. Free radical initiators such as peroxides are admixed withthe core composition so that on the application of heat and pressure, acomplex curing cross-linking reaction takes place.

The inner cover layer which is molded over the core is about 0.100inches to about 0.010 inches in thickness, preferably about 0.0375inches thick. The outer cover layer is about 0.010 inches to about 0.050inches in thickness, preferably 0.0300 inches thick. Together, the core,the inner cover layer and the outer cover layer combine to form a ballhaving a diameter of 1.680 inches or more, the minimum diameterpermitted by the rules of the United States Golf Association andweighing about 1.620 ounces.

Additional materials may be added to the cover compositions (both innerand outer cover layer) of the present: invention including dyes (forexample, Ultramarine Blue sold by Whitaker, Clark and Daniels of SouthPlainsfield, N.J.) (see U.S. Pat. No. 4,679,795); pigments such astitanium dioxide, zinc oxide, barium sulfate and zinc sulfate; and UVabsorbers; antioxidants; antistatic agents; and stabilizers. Further,the cover compositions of the present invention may also containsoftening agents, such as plasticizers, processing aids, etc. andreinforcing material such as glass fibers and inorganic fillers, as longas the desired properties produced by the golf ball covers are notimpaired.

The various cover composition layers of the present invention may beproduced according to conventional melt blending procedures. In the caseof the outer cover layer, when a blend of hard and soft, low acidionomer resins are utilized, the hard ionomer resins are blended withthe soft ionomeric resins and with a masterbatch containing the desiredadditives in a Banbury mixer, two-roll mill, or extruder prior tomolding. The blended composition is then formed into slabs andmaintained in such a state until molding is desired. Alternatively, asimple dry blend of the pelletized or granulated resins and colormasterbatch may be prepared and fed directly into the injection moldingmachine where homogenization occurs in the mixing section of the barrelprior to injection into the mold. If necessary, further additives suchas an inorganic filler, etc., may be added and uniformly mixed beforeinitiation of the molding process. A similar process is utilized toformulate the high acid ionomer resin compositions used to produce theinner cover layer.

The golf balls of the present invention can be produced by moldingprocesses currently well known in the golf ball art. Specifically, thegolf balls can be produced by injection molding or compression moldingthe inner cover layer about wound or solid molded cores to produce anintermediate golf ball having a diameter of about 1.50 to 1.67 inches,preferably about 1.620 inches. The outer layer is subsequently moldedover the inner layer to produce a golf ball having a diameter of 1.680inches or more. Although either solid cores or wound cores can be usedin the present invention, as a result of their lower cost and superiorperformance, solid molded cores are preferred over wound cores.

In compression molding, the inner cover composition is formed viainjection at about 380° F. to about 450° F. into smooth surfacedhemispherical shells which are then positioned around the core in a moldhaving the desired inner cover thickness and subjected to compressionmolding at 200° to 300° F. for about 2 to 10 minutes, followed bycooling at 50° to 70° F. for about 2 to 7 minutes to fuse the shellstogether to form a unitary intermediate ball. In addition, theintermediate balls may be produced by injection molding wherein theinner cover layer is injected directly around the core placed at thecenter of an intermediate ball mold for a period of time in a moldtemperature of from 50° F. to about 100° F. Subsequently, the outercover layer is molded about the core and the inner layer by similarcompression or injection molding techniques to form a dimpled golf ballof a diameter of 1.680 inches or more.

After molding, the golf balls produced may undergo various furtherprocessing steps such as buffing, painting and marking as disclosed inU.S. Pat. No. 4,911,451.

The resulting golf ball produced from the high acid ionomer resin innerlayer and the relatively softer, low flexural modulus outer layerprovide for an improved multi-layer golf ball which provides fordesirable coefficient of restitution and durability properties while atthe same time offering the feel and spin characteristics associated withsoft balata and balata-like covers of the prior art.

The present invention is further illustrated by the following examplesin which the parts of the specific ingredients are by weight. It is tobe understood that the present invention is not limited ;to theexamples, and various changes and modifications may be made in theinvention without departing from the spirit and scope thereof.

EXAMPLES

Several intermediate balls (cores plus inner cover layers) were preparedin accordance with conventional molding procedures described above. Theinner cover compositions were molded around 1.545 inch diameter coresweighing 36.5 grams such that the inner cover had a wall thickness ofabout 0.0675 inches, with the overall ball measuring about 1.680 inchesin diameter.

The cores utilized in the examples were comprised of the followingingredients: high cis-polybutadiene, zinc diacrylate, zinc oxide, zincstearate, peroxide, calcium carbonate, etc. The molded cores exhibitedRiehle compressions of about 60 and C.O.R. values of about 0.800. Arepresentative formulation of the molded cores is set forth below:

MATERIAL WEIGHT BR-1220 (high cis-polybutadiene) 70.70 Taktene 22O (highcis-polybutadiene) 29.30 React Rite ZDA (zinc diacrylate) 31.14 ZincOxide 6.23 Zinc Stearate 20.15 Limestone 17.58 Ground Flash 20.15 (20-40Mesh) Blue Masterbatch .012 Luperco 231XL .89 or Trigonox 29/40 Papi 94.50 ¹Blue Masterbatch consists of unknown compositions used only forinternal identification purposes and has no effect on physicalproperties.

The inner cover compositions designated herein as compositions A-Eutilized to formulate the intermediate balls are set forth in Table 7below. The resulting molded intermediate balls were tested to determinethe individual compression (Riehle), C.O.R., Shore C hardness, spin rateand cut resistance properties. These results are also set forth in Table7 below.

The data of these examples are the average of twelve intermediate ballsproduced for each example. The properties were measured according to thefollowing parameters:

Coefficient of restitution (C.O.R.) was measured by firing the resultinggolf ball in an air canon at a velocity of 125 feet per second against asteel plate positioned 12 feet from the muzzle of the canon. The reboundvelocity was then measured. The rebound velocity was divided by theforward velocity to give a coefficient of restitution.

Shore hardness was measured in accordance with ASTM test 2240.

Cut resistance was measured in accordance with the following procedure:A golf ball is fired at 135 feet per second against the leading edge ofa pitching wedge wherein the leading edge radius is {fraction (1/32)}inch, the loft angle is 51 degrees, the sole radius is 2.5 inches andthe bounce angle is 7 degrees.

The cut resistance of the balls tested herein was evaluated on a scaleof 1 to 5. The number 1 represents a cut that extends completely throughthe cover to the core. A 2 represents a cut that does not extendcompletely through the cover but that does break the surface. A 3 doesnot break the surface of the cover but does leave a permanent dent. A 4leaves only a slight crease which is permanent but not as severe as 3. A5 represents virtually no visible indentation or damage of any sort.

The spin rate of the golf ball was measured by striking the resultinggolf balls with a pitching wedge or 9 iron wherein the club head speedis about 105 feet per second and the ball is launched at an angle of 26to 34 degrees with an initial velocity of about 110 to 115 feet persecond. The spin rate was measured by observing the rotation of the ballin flight using stop action Strobe photography.

Initial velocity is the velocity of a ball when struck at a hammer speedof 143.8 feet per second in accordance with a test as prescribed by theU.S.G.A.

As will be noted, compositions A, B and C include high acid ionomericresins, with composition B further including zinc: stearate. CompositionD represents the inner layer (i.e. Surlyn 1605) used in U.S. Pat. No.4,431,193. Composition E provides a hard, low acid ionomeric resin.

The purpose behind producing and testing the balls of Table IV was toprovide a subsequent comparison in properties with the multi-layer golfballs of the present invention.

TABLE 7 Molded Intermediate Golf Balls A B C D E Ingredients of InnerCover Compositions Iotek 959 50 50 — — — Iotek 960 50 50 — Zinc Stearate50 — — — Surlyn 8162 — — 75 — — Surlyn 8422 — 25 — Surlyn 1605 — — 100 —Iotek 7030 — — — 50 Iotek 8000 — — — — 50 Properties of MoldedIntermediate Balls Compression 58 58 60 63 62 C.O.R. .811 .810 .807 .793.801 Shore C Hardness 98 98 97 96 96 Spin Rate (R.P.M.) 7,367 6,2507,903 8,337 7,956 Cut Resistance 4-5 4-5 4-5 4-5 4-5

As shown in Table 7 above, the high acid ionomer resin inner cover layer(molded intermediate balls A-C) have lower spin rates and exhibitsubstantially higher resiliency characteristics than the low acidionomer resin based inner cover layers of balls D and E.

Multi-layer balls in accordance with the present invention were thenprepared. Specifically, the inner cover compositions used to produceintermediate golf balls from Table 7 were molded over the solid cores toa thickness of about 0.0375 inches, thus forming the inner layer. Thediameter of the solid core with the inner layer measured about 1.620inches. Alternatively, the intermediate golf balls of Table 7 wereground down using a centerless grinding machine to a size of 1.620inches in diameter to produce an inner cover layer of 0.0375 inches.

The size of 1.620 inches was determined after attempting to mold theouter cover layer to various sizes (1.600″, 1.610″, 1.620″, 1.630″ and1.640″) of intermediate (core plus inner layer) balls. It was determinedthat 1.620″ was about the largest “intermediate” ball (i.e., core plusinner layer) which could be easily molded over with the soft outer layermaterials of choice. The goal herein was to use as thin an outer layeras necessary to achieve the desired playability characteristics whileminimizing the cost of the more expensive outer materials. However, witha larger diameter final golf ball and/or if the cover is compressionmolded, a thinner cover becomes feasible.

With the above in mind, an outer cover layer composition was blendedtogether in accordance with conventional blending techniques. The outerlayer composition used for this portion of the example is a relativelysoft cover composition such as those listed in U.S. Pat. No. 5,120,791.An example of such a soft cover composition is a 45% soft/55% hard lowacid ionomer blend designated by the inventor as “TE-90”. Thecomposition of TE-90 is set forth as follows:

Outer Cover Layer Composition TE-90 Iotek 8000 22.7 weight % Iotek 703022.7 weight % Iotek 7520 45.0 weight % White MB¹  9.6 weight % ¹White MBconsists of about 23.77 weight percent TiO₂; 0.22 weight percent UvitexOB, 0.03 weight percent Santonox R, 0.05 weight percent Ultramarine blueand 75.85 weight percent Iotek 7030.

The above outer layer composition was molded around each of the 1.620diameter intermediate balls comprising a core plus one of compositionsA-D, respectively. In addition, for comparison purposes, Surlyn® 1855(new Surlyn® 9020), the cover composition of the '193 patent, was moldedabout the inner layer of composition D (the intermediate ballrepresentative of the '193 patent). The outer layer TE-90 was molded toa thickness of approximately 0.030 inches to produce a golf ball ofapproximately 1.680 inches in diameter. The resulting balls (a dozenballs for each example) were tested and the various properties thereofare set forth in Table 8 as follows:

TABLE 8 Finished Balls 1 2 3 4 5 Ingredients: Inner Cover Composition AB C D D Outer Cover Composition TE-90 TE-90 TE-90 TE-90 Surlyn ® 9020Properties of Molded Finished Balls: Compressian 63 63 69 70 61 C.O.R..784 .778 .780 .770 .757 Share C Hardness 88 85 88 89 Spin (R.P.M.)8,825 8,854 8,814 8,990 8,846 Cut Resistance 3-4 3-4 3-4 3-4 1-2

As it will be noted in finished balls 1-4, by creating a multi-layercover utilizing the high acid ionomer resins in the inner cover layerand the hard/soft low acid ionomer resin in the outer cover layer,higher compression and increased spin rates are noted over the singlelayer covers of Table 7. In addition, both the C.O.R. and the Shore Chardness are reduced over the respective single layer covers of TableIV. This was once again particularly true with respect to themulti-layered balls containing the high acid ionomer resin in the innerlayer (i.e. finished balls 1-5). In addition, with the exception ofprior art ball 5 (i.e. the '193 patent), resistance to cutting remainsgood but is slightly decreased. As note above, the prior art ball of the'193 patent suffers substantially in durability (as well as inresiliency) in comparison to the balls of the present invention.

Furthermore, it is also noted that the use of the high acid ionomerresins as the inner cover material produces a substantial increase inthe finished balls overall distance properties. In this regard, the highacid ionomer resin inner covers of balls 1-3 produce an increase ofapproximately 10 points; in C.O.R. over the low acid ionomer resin innercovers of balls 4 and about a 25 point increase over the prior art balls5. Since an increase in 3 to 6 points in C.O.R. results in an averageincrease of about 1 yard in distance, such an improvement is deemed tobe significant.

Several other outer layer formulations were prepared and tested bymolding them around the core and inner cover layer combination to formballs each having a diameter of about 1.68 inches. First, B.F.GoodrichEstane® X-4517 polyester polyurethane was molded about the core moldedwith inner layer cover formulation A. DuPont Surlyn®9020 was moldedabout the core which was already molded with inner layer D. Similarproperties tests were conducted on these golf balls and the results areset forth in Table VI below:

TABLE 9 Finish Balls Ingredients: 6 7 Inner Cover Layer A D CompositionOuter Cover Layer Estanee ® 4517 Surlyn ® 9020 Composition Properites ofMolded Finished Balls: Compression 67 61 C.O.R. .774 .757 Shore CHardness 74 89 Spin (R.P.M.) 10,061 8,846 Cut Resistance 3-4 1-2

The ball comprising inner layer formulation D and Surlyn® 9020identifies the ball in the Nesbitt 4,431,193 patent. As is noted, theexample provides for relatively high softness and spin rate though itsuffers from poor cut resistance and low C.O.R. This ball isunacceptable by today'as standards.

As for the Estanes X-4517 polyester polyurethane, a significant increasein spin rate over the TE-90 cover is noted along with an increasedcompression. However, the C.O.R. and Shore C values are reduced, whilethe cut resistance remains the same.

Furthermore, both the Estane® X-4517 polyester polyurethane and theSurlyn® 9020 were relatively difficult to mold in such thin sections.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon reading and understanding the proceeding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

I claim:
 1. A golf ball comprising: a core; an inner cover layer moldedon said core, the inner cover layer comprising a high acid ionomerincluding at least 16% by weight of an alpha, beta-unsaturatedcarboxylic acid; and an outer cover layer molded on said inner coverlayer, said outer cover layer comprising a relatively soft polymericmaterial selected from the group consisting of low flexural modulusionomer resins and non-ionomeric thermoplastic elastomers.
 2. A golfball comprising: a core; an inner cover layer molded on said core; andan outer cover layer molded on said inner cover layer, said outer coverhaving a lower Shore C hardness than the inner cover layer and a cutresistance of at least 3, said outer cover layer comprising a relativelysoft polymeric material selected from the group consisting of lowflexural modulus ionomer resins and non-ionomeric thermoplasticelastomers.
 3. A golf ball according to claim 2, wherein said golf ballhas a coefficient of restitution of at least 0.770.
 4. A golf ballaccording to claim 2, wherein said outer cover layer has a Shore Chardness of no more than
 88. 5. A golf ball according to claim 2,wherein said outer cover layer has a Shore C hardness of 74-88.
 6. Agolf ball according to claim 2, wherein said core with said inner coverlayer molded thereon comprise an intermediate ball, and saidintermediate ball has a coefficient of restitution of greater than0.801.
 7. A golf ball comprising: a core; an inner cover layer molded onsaid core; and an outer cover layer molded on said inner cover layer,said outer cover layer comprising a relatively soft polymeric materialselected from the group consisting of low flexural modulus ionomerresins and non-ionomeric thermoplastic elastomers; said golf ball havinga Riehle compression of 63 or more.
 8. A golf ball according to claim 7,wherein the golf ball has a Riehle compression of about
 70. 9. A golfball according to claim 7, wherein the golf ball has a Riehlecompression of about 63-70.
 10. A golf ball according to claim 7,wherein said core with said inner cover layer molded thereon comprise anintermediate ball, and said intermediate ball has a coefficient ofrestitution of greater than 0.801.
 11. A golf ball comprising: a core;an inner cover layer molded on said core, said inner cover layer havinga Shore C hardness; and an outer cover layer molded on said inner coverlayer, said outer cover layer having a Shore C hardness which is atleast 10 points lower than the Shore C hardness of said inner coverlayer, said outer cover layer comprising a relatively soft polymericmaterial selected from the group consisting of low flexural modulusionomer resins and non-ionomeric thermoplastic elastomers.
 12. A golfball according to claim 11, wherein the outer layer has a Shore Chardness which is 10-24 points lower than the Shore C hardness of saidinner cover layer.
 13. A golf ball according to claim 11, wherein saidgolf ball has a cut resistance of at least
 3. 14. A golf ball accordingto claim 11, wherein said core with said inner cover layer moldedthereon comprise an intermediate ball, and said intermediate ball has acoefficient of restitution of at least 0.801.
 15. A golf ballcomprising: a core; an inner cover layer molded on said core to form aninner ball having a Riehle compression; and an outer cover layer moldedon said inner cover layer, said outer cover layer comprising arelatively soft polymeric material selected from the group consisting oflow flexural modulus ionomer resins and non-ionomeric thermoplasticelastomers; said golf ball having a Riehle compression which is at least5 points higher than the Riehle compression of said inner ball.
 16. Agolf ball according to claim 15, wherein the Riehle compression of saidgolf ball is about 5-9 points higher than the Riehle compression of saidinner ball.
 17. A golf ball according to claim 15, wherein said golfball has a cut resistance of at least
 3. 18. A golf ball according toclaim 15, wherein said core with said inner cover layer molded thereoncomprise an inner ball, and said inner ball has a coefficient ofrestitution of at least 0.801.
 19. A golf ball according to claim 2,wherein said core is a solid core.
 20. A golf ball according to claim 2,wherein said core is a wound core.